Limited range transformer with a tap changing system



' Dec. 22, 1970 J, CARLQ 3,550,054

LIMITED RANGE TRANSFORMER WITH A TAP CHANGING SYSTEM Filed May 15. 19695 Sheets-Sheet 1 ELIOT JOSEPH CARLO Dec. 22, 1970 Filed May 15, 1969 E.J. CARLO LIMITED RANGE TRANSFORMER WITH A TAP CHANGING SYSTEM 5Sheets-Sheet 2 26 *v 43 95&% AZ 96 93& 29 35% I \36 94 mygxr/ I 49 5 8 3x mm 22- 1 zmummll 1 I! 8 F 16.3 1 7| 66 65 I INVENTOR. ELIOT JOSEPH CARLO E. J. CARLO Dec. 22, 1970 LIMITED RANGE TRANSFORMER WITH A TAPCHANGING SYSTEM 15 1969 OUT Filed FIG-5 4 4 4/////// m 4 ww whfi J W Q 6k M 5 U I O m W wk f ImWUWWW I MM w R w m w M 0 INVENTOR.

ELIOT JOSEPH CARLO jw gafl 31 6511,

Dec. 22, 1970 CARLO 3,550,054-

LIMITED RANGE TRANSFORMER WITH A TAP CHANGING SYSTEM Filed May 15, 19695 Sheets-Sheet 5 :09 no 420 1 1 I090 H00 1/54 H614 El y 553 A38 M 52 BRI33 Ea Inventor ELIOT JOSEPH CARLO by.- 3.201 4 04 W.

United States Patent 3,550,054 LIMITED RANGE TRANSFORMER WITH A TAPCHANGING SYSTEM Eliot Joseph Carlo, 138 McMurchy St. S., Brampton,Ontario, Canada Filed May 15, 1969, Ser. No. 824,919 Int. Cl. H01f 21/02US. Cl. 336-120 6 Claims ABSTRACT OF THE DISCLOSURE A tap changingsystem for transformers having a pair of cylindrical-shape core memberswith a pair of notches on opposite sides of each core member definingspaced apart semi-cylindrical legs joined at one end by a base, one ofthe core members being rotatable relative to the other for mutualangular displacement about a common axis. The tap system has at leastone field winding on each leg of the core members with a plurality orcoil sections, a tap connection at each end of each coil section andswitching means for selectively connecting each tap connection to anadjacent tap connection of a coil section of the field windings on thesame core member whereby the coil sections are connected in series orparallel or a combination of both.

This invention relates to a control device for providing continuousadjustment of electrical magnitudes, such as amperage and voltage.

In the past, voltages have been controlled in some instances by the useof transformers with primary and secondary windings, mounted upon ironcores, which are movable with respect to one another to vary theinduction. However, due to the requirements for such movement, it isonly possible to operate such devices in a relatively inefiicientmanner. In addition, they occupied a great deal of space.

Similarly, earlier devices are known in which amperag s have beencontrolled in a similar manner with the addition of a so-called magneticshunt on the above noted iron cores. These devices are highly expensiveand operate in a relatively ineflicient manner.

One known form of control device employing movable primary and secondarywinding units is disclosed in French Letters Patent No. 1,517,620. Inthis device, primary and secondary windings are mounted on a pair ofjuxtaposed rectangularly-shaped iron cores having spaced apart legsparallel with one another, and the primary and secondary winding unitsare movably associated end to end with the exposed end faces of theirrespective iron cores in contact with one another. The magnetic fluxlines close through the iron in the exposed end surfaces of the ironcores even during rotation of one iron core relative to the other. Whilethis device appears to be greatly superior to such earlier devices whenused in the maximum and minimum positions, practical experiments haveproven that it too is subjected to very serious drawbacks. Thus it hasbeen found for example, that when the device is rotated between themaximum and minimum positions, under constant load conditions, andoperated in the intermediate position, the device overheats and thedevice, if not securely locked in position tends to vibrate and hum. Asa result, it is necessary to operate the control device on anintermittent basis to prevent overheating. The specific reason for theseshortcomings are not fully known, but it is believed to be due to thefact that as the primary and secondary winding units are moved relativeto one another, the area of contact between the exposed end surfaces ofthe juxtaposed legs is changed, and most of the magnetic flux lines are"Ice not closed through iron when rotated between the minimum andmaximum position. In addition, there may also be other contributingfactors such as the factor that the secondary windings themselves, beingof generally rectangular shape are not cut by all the induced magneticflux lines.

Accordingly, it is an object of the present invention to provide acontrol device of the type described in which cylindrical iron cores areplaced in a juxtaposed relationship having spaced apart legs which arecurved in a generally semi-cylindrical manner and end surfaces incontact with opposite end surfaces whereby one iron core can be rotatedrelative to the other and the area of contact between adjacent endsurfaces is not appreciably decreased. The primary and secondarywindings positioned on the semi-cylindrical legs of the iron cores areformed to conform to the curved shaping of the leg to permit electriccurrent to be generated in the windings by the magnetic flux of linesflowing in the legs of the cores. When one iron core is rotated relativeto the other from the minimum to the maximum position, there is aminimal change in area of contact between the end surfaces such that theiron cores will not overheat under load and no load conditions and thevibrations and hum disappear.

It is an object of the present invention to provide a control devicehaving the foregoing advantages which is of reduced size in relation toearlier devices, thereby making it more economical to manufacture andopening up a wide variety of applications.

It is another object of this invention to provide a control devicehaving the foregoing advantages which is readily adaptable to providedifferent characteristics of a voltage-amperage load curve by rotationof the one iron core relative to the other and also rotation of amagnetic shunt relative to the two stationary iron cores according tothe requirements of the job at hand.

It is still another object of this invention to provide a control devicehaving the foregoing advantages and incorporating asymmetricarrangements of secondary windings in such a manner that the outputvoltage from the inductively coupled secondary windings can be varied bya fixed amount above and below the value of the input voltage into theprimary windings.

The foregoing and other objectives will become apparent from thefollowing description of a preferred embodiment of the invention whichis given hereby way of example only with reference to the followingdrawings, in which like reference devices refer to like parts thereofthroughout the various views and diagrams and in which:

FIG. 1 is an exploded upper perspective view of a control device partlybroken away according to the invention;

FIG. 1A is an exploded perspective view of the control device showingthe engaging surfaces of the core members;

FIG. 2 is an exploded perspective view of the core members and fieldwindings used in the control device;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is a schematic diagram of the field windings inductively coupledon the core members;

FIG. 5 is a schematic diagram of the field windings and the core membersshown in a rotated position from the position shown in FIG. 4;

FIG. 6 is a schematic diagram showing the field windings galvanicallyconnected in the control device to control current;

FIG. 7 is a schematic diagram of the field windings galvanicallyconnected in a position from the position shown in FIG. 6;

FIG. 8 is a schematic diagram showing the field windings galvanicallyconnected in a control device to control voltage;

FIG. 9 is a schematic diagram showing the field windings in a 180position from that shown in FIG. 8;

FIG. 10 is a crosssectional view of an alternate embodiment of theinvention for use in the field of arc welding;

FIG. 11 is a cross-sectional view taken along the line 1111 of FIG. 10;

FIG. 12 is a view similar to FIG. 11 but showing the core membersrotated relative to the semi-annular bodies;

FIG. 13 is a view similar to FIG. 12 showing the semi-annular ironbodies rotated 60 from the position shown in FIG. 11;

FIG. 14 is a schematic diagram showing the field windings of a lowvoltage transformer connected to sockets to permit differentarrangements of the windings;

FIG. 15 is a schematic diagram showing the field windings of a limitedrange transformer to produce an output voltage which is a fixed amountabove the input voltage; and

FIG. 16 is a schematic diagram showing the field windings of a limitedrange transformer to produce an output voltage being a fixed amountbelow the input voltage.

It should be noted that the invention will be described in associationwith a core type transformer having two legged iron cores, however, theinvention can be used in association with other types of transformersincluding shell type transformers with three phase construction. Thefield windings will preferably be arranged on the middle leg of eachiron core. The number of degrees of rotation of one iron core relativeto the other to define the control range of the device can be found byexperimentation.

Referring now to the drawings, FIGS. 1 and 2, illustrate a core typetransformer indicated by the general character 20. The transformer 20has a pair of cylindrical core members 21 and 22 with identicaldiameter, width and depth shown best in FIG. 2. The core members aremade from magnetic or electrical conductive material such as strips ofhigh grade silicone steel or the like which have been concentricallywound into a high circular spiral. The core members will now be referredto as iron cores 21 and 22. Notches 23 and 24 are cut on opposite sidesof the core 21 to form a pair of spaced apart semi-cylindrical shapedlegs 25 and 26 joined at one end by a base 27. The legs 25 and 26 haveexposed end surfaces or polar surfaces 28 and 29 respectively. The ironcore 22 has notches 30 and 31 cut on opposite sides of the core 22 toform spaced apart semi-cylindrical shaped legs 32 and 33 joined at oneend by a base 34. The legs 32 and 33 have exposed end surfaces or polarsurfaces 35 and 36 respectively. The polar surfaces 28, 29, 35 and 36are preferably identical in area and each is enclosed by spaced apartouter curved edge 37 and inner curved edge 38 which are joined at theirfree ends by end edges 39 and 40 preferably in the same plane. The ironcores 21 and 22 are arranged for mutual angular displacement around acommon axis 41. The iron core 22 will be described as the stationaryiron core and iron core 21 will be described as the rotating iron core.The rotating iron core 21 is moved relative to the stationary iron core22 for angular displacement. It should be noted that it is possible torotate the iron core 22 relative to the iron core 21 also.

Secondary field windings 42 and 43 shown best in FIG. 2, arekidney-shaped in cross-section and are dimensioned to snugly fit on thesemi-cylindrical legs 25 and 26 respectively of the iron core 21. Eachfield winding 42 and 43 contains an equal number of turns of copper orthe like wire therein. The winding 42 has two terminals 44 and 45. Thefield winding 43 has two terminals 46 and 47. The secondary fieldwindings 42 and 43 are insulated from the rotating iron core 21.

Primary field windings 48 and 49 are kidney-shaped in cross-section andare dimensioned to snugly fit on the semi-cylindrical shaped legs 32 and33 on the stationary iron core 22. The field windings 48 and 49 have anequal number of turns of copper or the like wire therein. The fieldwinding 48 has two terminals 50 and 51; the field winding 49 has twoterminals 52 and 53. The primary field windings 48 and 49 are insulatedfrom the stationary iron core 22.

Preferably the field windings 42, 43, 48 and 49 each have an equalnumber of turns of copper wire and are arranged symmetrically about thecommon axis 41 and about the plane of the touching polar surfaces sothat the angular displacement of the rotating iron core 10 relative tothe stationary iron core 11 provides a substantially linearcharacteristic of control for current or voltage as desired. The fieldwindings can also be wound assymetrically about the common axis 41 andthe rotational plane of the polar surfaces to provide any desiredcharacteristics of control.

The secondary windings 42 and 43 are connected in series by connectingthe terminals 44 and 46 and are wound on the legs 26 and 28 in such amanner to induce fields as shown in FIG. 4 by arrows 54 and 55respectively. The primary windings 48 and 49 are connected in series byjoining terminals 50 and 52 and are Wound on the legs 32 and 33 in sucha manner to induce fields as shown in FIG. 4 by arrows 56 and 57respectively. The primary windings are shown inductively coupled to thesecondary windings in FIGS. 4 and 5.

As shown best in FIG. 1, the stationary iron core 22 with the primaryfield windings 48 and 49 thereon, are embedded in a cylindrical body 58preferably made of synthetic resin or the like. A circular groove 59 isformed in the upper portion of the body 58 with parallel side walls 60and 61 shown best in FIG. 1A. The rotating iron core 21 with thesecondary field windings 42 and 43 are embedded in a cylindrical body 62preferably made of synthetic resin or the like in such a manner that thelower portion of the semi-cylindrical shaped legs 25 and 26 extendoutwards from the lower end of the resin body 62 to fit in the circulargroove 59 in the cylindrical body 58.

The groove 59 permits the legs 25 and 26 of the rotating iron core 21 tobe aligned with the legs 32 and 33 of the stationary iron core 22 whenthe cylindrical resin body 62 is placed on the cylindrical resin body 58in a juxtaposed relationship.

The cylindrical shape of the iron cores and the kidney shape of thefield windings permits the opening in the center of the cylindricalresin bodies 58 and 62 to be used to hold the cylindrical bodies 58 and62 rotatably in their juxtaposed relationship. A center post andsecuring means indicated generally as 63 has a hollow center post '64extending through the opening in the bodies 58 and 62 along the commonaxis 41. A flange is connected to the lower end of the post 64 by asecuring means 66. The cylindrical resin body 58 is secured to theflange 65 to prevent it from rotating. A rigid member 67 is secured tothe upper end of the post 64 with a rotatable knob 68 passed through thefree end thereof. A first gear 69 is connected to the lower portion ofthe knob 68 and has teeth which interengage with teeth on a second gear70 secured on the cylindrical resin body 62 to permit an operator torotate body 62 manually by rotating the knob 68. Legs 71 connected tothe flange 65 raise the cylindrical body 58 off a base B to permit airto pass through the center opening of the hollow post 64 to cool thewindings and iron cores.

The terminals 45 and 47 of the secondary windings 42 and 43 are extendedoutside the cylindrical resin body 62 to a female socket 72 attached onthe outside surface of the cylindrical resin body 62. A plug 73 withprongs 74 and 75 is adapted to be inserted in the socket 72 andconnected to the prongs 74 and 75 are load terminals 76 and 77 by lines78 and 79 respectively. A load 80 is connected to the terminals 76 and77 thereby connecting the load 80 across the terminals 45 and 47 of thesecondary windings 42 and 43.

The terminals 50 and 52 of the primary wind-ings 48 and 49 are extendedoutside the cylindrical resin body 58 to a female socket 81 attached onthe outside surface of the cylindrical resin body 58. A plug 82 withprongs 83 and 84 is adapted to be inserted in the socket 81 andconnected to the prongs 83 and 84 and terminals 85 and 86 by lines 87and 88 respectively. An electrical source 89 is connected to theterminals 85 and 86 thereby connecting the electrical source 89 acrossthe termi nals 50 and 52 of the primary windings 48 and 49.

The primary and secondary field windings can also be galvanicallyconnected to control current and voltage as shown in FIGS. 6 to 9. Tocontrol cur-rent the terminals are connected as shown in FIGS. 6 and 7.The secondary windings 42 and 43 are connected in series by placing theterminals 45 and 47 in contact with a tube 90 made of copper or thelike, attached to the inner surface of the cylindrical resin body 62.The terminal 44 of the secondary winding 42 is connected to an annularflange 9011 made of copper or the like attached to the upper end of thecylindrical resin body 62 and the center post 64 is in contact with theflange 90a. The primary windings 48 and 49 are connected in series byplacing the terminals 50 and 52 in contact with a tube 91 of copper orthe like attached to the inner surface of the cylindrical resin body 58.The terminal 53 of the primary winding 49 is connected to an annularflange 91a made of copper or the like attached to the lower end of thecylindrical resin body 58 and the center post 64 is in contact with theflange 91a. The terminal 44 of the secondary winding 42 is then inmetallic contact with the terminal 53 of the primary winding 49 throughthe flange 90a, center post 64 and flange 91a.

To control voltage, the terminals of the primary and secondary fieldwindings are galvanically connected as shown in FIGS. 8 and 9. The tubes90 and 91 are placed in contact. The input voltage V is connected to theprimary field windings by connecting the input terminal 85 to theterminal 50 of the primary field winding 48 by a line 92 and the inputterminal 86 to the copper tube 91 and terminal 52 of the primary winding49 by a line 92a. The primary field windings 48 and 49 are connected inseries by connecting terminals 51 and 52 to the annular flange 91a. Thesecondary field windings 42 and 43 are connected in series by connectingterminals 44 and 46 to the annular flange 90a. The secondary fieldwindings are connected in series with the primary field windings byconnecting terminal 45 of the field winding 42 to the tube 90 which isin contact with the tube 91. The output voltage V is between theterminal 47 of the secondary field winding 43 and the terminal 50 of theprimary field winding 48.

The iron cores 21 and 32 have circular cross-sections and at the polarsurfaces 28, 29, and 36, the circular cross-sectional areas areidentical. When the iron cores 21 and 22 are assembled in the juxtaposedrelationship, the polar surfaces 2 8, 29, 35 and 36 in contact lie in aplane disposed transversely to the common axis 41. In this position, theouter and inner edges 37 and 3 8 and of adjacent polar surfaces 28, 32and 29, 26 are aligned. When the polar surfaces are completely incontact, the end edges 39 and of the adjacent polar surfaces are alsoaligned and the maximum number of magnetic flux lines are permitted toclose through iron.

When the rotating iron core 21 is rotated relative to the stationaryiron core for mutual angular displacement around the common axis 41, thesemi-cylindrical legs and the circular cross-sectional area of the polarsurfaces ensures that the contact area of the polar surfaces is notappreciably decreased and most of the magnetic flux lines are permittedto still close through iron. A portion of each polar surface is over anair space between the adjacent end edges of the polar surfaces on thesame iron core but the contact area is only decreased by approximatelyfive percent in any angularly displaced mutual position of the ironcores 21 and 22 about the common axis 41. The outer and inner edges 37and 38 are always aligned thus providing that the maximum contact areais provided between polar surfaces for magnetic flux lines between theiron cores 21 and 22.

The circular cross-section of the cylindrical iron cores 21 and 22 alsoprovides that all points on the outer edges 37 of the polar surfaces arean equal distance away from the common axis 41.

Complete regulation of a core type transformer can be attained byconnecting the secondary field windings 42 and 43 on the rotating ironcore 21 inductively or galvanically with the primary field windings 48and 49 on the stationary iron core 21. If the secondary windings areonly inductively coupled to the primary windings, a complete range ofcontrol is obtained with a rotation of the rotating iron core 21relative to the stationary iron core 22. In the minimum position, theoutput voltage at the terminals 44 and 46 of the secondary fieldwindings 42 and 43 respectively is generated in the secondary fieldwinding by induction, The voltage in the secondary windings is equal tothe input voltage at the terminals 51 and 53 of the primary fieldwindings 48 and 49 respectively. When the iron core 21 is rotated 90=relative to the sta tionary iron core 22, the rotating iron core 21closes the main magnetic flux lines entirely and there is no outputvoltage generated from the field windings 42 and 43 by induction.

If the primary and secondary windings are galvanical- 1y connected tocontrol voltage, a complete range of control is obtained with rotation.In the minimum position shown in FIG. 9, the primary and secondarywindings are working against one another giving a zero voltage at theoutput terminals 45 and 52. After the 90 rotation, the main magneticflux is closed through the rotating iron core 21 and no voltage isgenerated in the secondary field windings 42 and 43 by induction. Thecurrent flowing through the primary and secondary windings is at amaximum and the primary voltage appears at the output terminals 47 and50. As the rotating iron core 21 is rotated from the 90 position to the180 position (maximum position) the primary and secondary windings beginto work together and a voltage is gradually induced into the secondarywindings 42 and 43 which is added to the primary voltage at theterminals 47 and 50. The maximum voltage is attained at the 180 positionshown in FIG. 8.

If the number of turns in the secondary windings 42 and 43 is equal tothe number of turns in the primary windings 48 and 49, then the voltageat the output terminals 47 and 50 will be double the input voltage atthe input terminals 85 and 86. Therefore, with the primary and secondarywindings galvancially connected, a voltage control is possible from zerovalue to double the input voltage.

In operation, to control amperage through the galvanically connectedfield windings on a core type transformer, the primary and secondarywindings are connected as shown in FIG. 6. The current comes in atterminal 46 of the secondary field winding 43 flows through the primaryand secondary field winding and out at terminal 51 of the primary fieldwinding 48. The induced fields in the secondary windings are opposite tofields of the primary field windings and cancel each other. The currentflowing through primary and secondary field windings is at a miximumwith no induced voltage being formed in the primary and secondary fieldwindings. When the rotating iron core 21 is rotated 180 relative to thestationary iron core 22 to the position shown in FIG. 7, the inducedfields are aiding one another. The reactance is at a maximum and thecurrent flowing through the primary and secondary field windings is at aminimum under constant load conditions. Between the maximum and minimumpositions, a linear control of the amperage is possible.

To control voltage to a load, the primary and secondary field windingsmay be inductively coupled as shown in FIGS. 4 and 5 or galvanicallyconnected as shown in FIGS. 8 and 9. With the primary and secondarywindings inductively coupled, the output voltage at the terminals 45 and47 generated in the secondary field windings 42 and 43 by induction isequal to the input voltage at the terminals 50 and 52 of the primaryfield windings 48 and 49. When the rotating iron core 21 has been r0.-tated 90 relative to the stationary iron core 22, the rotating iron core21 closes the main magnetic flux lines entirely and there is no outputvoltage generated from the secondary field windings 42 and 43 byinduction.

When the primary and secondary fields are galvanically connected asshown in FIG. 9, the primary and secondary field windings are workingagainst each other and cancel out each other. Thus zero voltage appearsbetween the output terminals 47 and 50 of the field windings. Byrotating the rotating iron core 21 from the minimum position to the 90position the main flux closes here and there is no induced voltage inthe secondary field windings. However, the entire primary voltageappears at the out put terminals 47 and 50 of the field windings.

When the rotating iron core 21 is rotated from the 90 position to the180 position relative to the stationary iron core 22, a voltage isinduced in the secondary field windings to add to the voltage in theprimary field windings. At the 180 position a voltage equal to the inputvoltage is generated in the secondary field windings and this is addedto the primary voltage inserted so that an output voltage is obtained atthe output terminals 47 and 50 which is double the input voltage.Between the minimum and maximum positions, a linear control of thevoltage is possible.

It should be noted that in manufacturing the rotating and stationaryiron cores 21 and 22 they should prefer ably be stress annealed so thatthe cores will hold their desired shape when used in the transformers20. The cores 21 and 22 are stress annealed by subjecting them to heatat a temperature of 800 centigrade for a period of four hours.

In order to increase the contact area of adjacent polar surfaces toreduce the hum noise in the transformer 20, a first pair of semi-annulariron bodies 93 and 94 preferably made of laminated high grade siliconsteel or the like are embedded in the cylindrical resin body 58 andplaced in contact with the outer curved surfaces 37 of thesemi-cylindrical legs 32 and 33 of the stationary iron core 22. Theupper ends of the semi-annular bodies 93 and 94 are positioned above thepolar surfaces 35 and 36 of the legs 32 and 33 to permit the polarsurfaces 28 and 29 of the legs 25 and 26 of the rotating iron core 21respectively to make contact with the adjacent polar surface on thestationary iron core 22 while the outer surfaces 37 of the legs 25 and26 are placed in contact with the semi-annular iron bodies 93 and 94.

The iron bodies 93 and 94 increase the depth of the rotating andstationary iron bodies 21 and 22 in the region of the polar surfaces 28,29, 35 and 36 to permit the magnetic flux lines to close through iron.If desired, a second pair of semi-annular bodies 95 and 96 preferablymade of laminated high grade silicon steel or the like may be placed incontact with the inner curved surfaces 38 of the semi-cylindrical legsin the same plane as the first pair of semi-annular iron bodies 93 and94 to increase the depth of the rotating and stationary iron bodie 21and 22 in the region of the polar surfaces 28, 29, 35 and 36.

Another embodiment of the invention is shown in FIG. 10, where thetransformers 20 can be used in the field of arc welding. It is desirableto have a control device according to the invention which permits anoperator to control current and voltage from a single transformer.

For manual arc Welding a drooping voltage-amperage characteristic curvewith the voltage being the ordinate and the amperage being the abscissa,is desired where an operator can control the welding amperage. When theamperage is zero, the voltage is called an open-circuit voltage. Forautomatic or machine arc-welding, the characteristic voltage-amperagecurve, is a very flat curve where the operator can control the voltageand current.

The transformer 20 with the primary and secondary field windingsinductively coupled as previously described is suitable for use in arcwelding, but is improved with the following alterations. The outersemi-annular iron bodies 93 and 94 are not embedded in the cylindricalresin body 58 but are rotatably held between the cylindrical resinbodies 58 and 62 in their juxtaposed relationship. A cylindrical lug 97made of resin or the like is connected to an outer surface 98 of thesemi-annular bodies 93 and 94 and extends out from the cylindrical resinbodies 58 and 62 to permit an operator to hold a ree end 99 of the lug97 and manually rotate the semiannular bodies 93 and 94. With a largertransformer 20 preferably the semi-annular bodies 93 and 94 will berotated by a worm gear (not shown) from an electric drive mechanism (notshown) engaging a semi-threaded portion (not shown) on the free end 99of the lug 97.

In operation for manual arc welding, the operator connects up the load80 to the output terminals 45 and 47 of the secondary field windings 42and 43 and connects the electrical source 89 to the input terminals and52 of the primary field windings 48 and 49. To alter the weldingamperage desired, the semi-annular bodies 93 and 94 are rotated inrelationship to the rotating and stationary iron bodies 21 and 22 asshown in FIG. 13. The semi-annular bodies 93 and 94 act as magneticshunts directing the magnetic flux lines going to the rotating iron core21 back to the stationary iron core 22.

For automatic arc welding, the operator rotates only the rotating ironcore 21 relative to the stationary iron core 22 to obtain the flatcharacteristic curve. A complete conrol preferably is obtained between amaximum and minimum position by a rotation of approximately 50 ordegrees.

It should be noted that any combination of the characteristic curvesmentioned above can be obtained by the operator using a combination ofthe two procedures. If the operator wishes to operate the transformer 20in an intermediate position between the maximum and minimum positions,there is no problem of overheating, as the greatest number of magneticflux lines are closed through iron. Also the operator can adjust thevoltage and amperage under constant load conditions and can disconnectthe electrical source 89 whe working at an intermediate position betweenthe maximum and minimum positions.

Another embodiment of the invention is shown schematically in FIGS. 14to 16 where the transformer 20 can be used with a tap changing system aseither a low voltage transformer with an isolated secondary or as alimited range transformer. Known transformers using carbon brushes arelimited to the maximum current rating that can be used before the carbonbrushes overheat and burn.

As a low voltage transformer, as shown schematically in FIG. 14, thesecondary field windings 42 and 43 are inductively coupled to theprimary field windings 4'8 and 49. The copper Wire used in the secondaryfield windings 42 and 43 should be able to carry the maximum currentdesired. Each secondary field winding 42 and 43 is divided into two coilsections 42a, 42b and 43a, 43b respectively. Each primary field winding48 and 49 is divided into two coil sections 48a, 48b and 49a, 49brespectively. Tap connections are made at each end of the coil section.The individual coil sections of the primary or secondary field windingsare selectively interconnected by a switching means to have the coiledsections connected in series or parallel or a combination of both. Thusin the primary windings different input voltages can be used. Also inthe secondary winding three ranges of low voltages can be obtained withthe different primary voltages.

For example, eight tap connections 103 to 110 can be made to thesecondary coil sections 42a, 42b and 43a and 43b with substantially thesame potential difference between adjacent tap connections. The tapconnections 103 to 110 are attached to eight female terminals 103a to110a in a secondary receptacle 111. The tap connections 103 to 110 areattached to the female terminals as follows: tap 103 to 103a; tap 104 to106a; tap 105 to 104a; tap 106 to 105a; tap 107 to 107a; tap 108 to110a; tap 109 to 108a; and tap 110 to 109a. A plug 112 with eight prongs.113 to 120 can be inserted in the receptacle 111. The pron'gs 113 to120 can be interconnected in different ways to arrange the coil sectionof the secondary field windings in series or parallel or a combinationof both. The plug 112 shown in FIG. 14 has the prongs interconnected insuch a manner that the coil sections are connected in parallel.

The primary coil sections 48a, 48b and 49a and 491) have eighttapconnections 121 to 128 attached to eight female terminals 121a to128a in a primary receptacle 129. The tap connections 121 to 128 areattached to the female terminals as follows: tap 121 to 121a; tap 122 to124a; tap 123 to 122a; tap 124 to 123a; tap 125 to 125a; tap 126 to128a; tap 127 to 126a; and tap 12:8 to 127a. A pluig 130 with eightprongs 131 to 138 is inserted in the receptacle .129. The prongs can beinterconnected in different ways to arrange the primary coil sections inseries or parallel or a combination of both to receive one of the threedesired input voltages. The two plugs 130 and 130 shown in FIG. 14 areinterconnected to arrange the coil sections in series and in combinationof series and parallel respectively.

In operation, the operator will insert the correct plug 130 into theprimary receptacle 129 for the desired input voltalge and also willinsert the desired plug 112 into the secondary receptacle 111 for thedesired output voltage. Linear control of the output voltage from thesecondary winding is possible between zero volts and the maximum outputvolts through a 90 rotation of the rotating iron core 21 relative to thestationary iron core 22.

An example of using the transformer 20 as a low volta ge transformerwith an isolated secondary having a maximum 3 k.v.a. rating is set outin the following chart:

If desired, the rotating iron core 21 can :be left in an intermediateposition between the maximum and minimum positions without the ironcores overheating. Also, if the transformer 20 is overloaded, say withfive times the maximum load the overload capacity of this transformer issuch that the maximum time the transformer can be subjected to thisoverload is over two minutes. Also with repetitive overloads, thetransformer need not be turned off for any set length of time asexcessive temperature build up is not a problem.

As a limited range transformer, the secondary field windin gs aregalvanically connected to the primary field windings as previouslydescribed with reference to FIGS. 8 and 9 to control voltage. It shouldbe noted that the inducttively coupled low voltage transfonmer describedhereinbefore can be changed over to a galvanically connected limitedrange transformer by connecting tap 104 of the secondary field winding43 to the tap 128 of the primary field winding 49. The copper wire usedin the secondary winding must be able to carry the maximum current whichwill flow through the secondary field Wind ings. The primary windingsare also used as a portion 10 of the secondary winding, as the currentpassing through the primary windings is 180 out of phase with thesecondary current generated in the same windings and the resultantcurrent is a value which is less than the secondary current and can becarried by the primary field windings.

A limited range transformer is used by an operator to give a voltagedifferential which is above and below the value of the input voltagewithin a predetermined voltageamperage value. With the primary andsecondary windings galvanically connected, the input voltage V betweenterminals 50 and 52 appears as the output voltage VOUT between terminals50 and 45 increased or decreased by the voltage generated in thesecondary field windings. The input voltage can be altered for examplebetween volts to 480 volts b-y substitutin g different plugs in theprimary receptacle 129 to obtain a limited range transformer having avoltage-amperage rating up to 51 k.v.a. on the same transformer 20.

In operation, the operator inserts the correct plug 130 into the primaryreceptacle 129 for the desired input volta'ge V to be used. Also, thecorrect plug 112 is inserted into the secondary receptacle 111 to givethe desired control range of voltages about the input voltage. As shownin FIG. 15, the voltage generated in the secondary field windin gs isaiding the voltage in the primary field windings and the output voltageV in the sum of the two voltages. As shown in FIG. 16, the rotating ironcore 22 is rotated relative to the stationary iron core 21 from theposition shown in FIG. 15 and the voltage gen erated in the secondaryfield windings is working against the voltage in the primary fieldwindings and the output voltage V is the primary voltage V minus thevoltage generated in the secondary field windings. A linear control ofvoltage is possible between the maximum and minimum positions.

An example of using the transformer 20 as a limited range transformerhaving a maximum 51 k.v.a. is set out in the following chart:

It should be noted that the regulation of V is independent of thedirection in which the rotating iron core 21 with the secondary fieldwindings is rotated. By a rotation of from 0 to 180 the limited range ofoutput voltage is obtained. The operator can continue to rotate in thesame direction going from 180 to 360 and a linear control over thelimited range of output voltage is obtained from the maximum to theminimum position.

The foregoing is a description of a preferred embodiment of theinvention only. The invention is not to be taken as limited to any ofthe specific features described, but comprehends all such variations ascome within the spirit and scope of the claims.

What I claim is:

1. A tap changing system for transformers having a pair of core membersof magnetic or electrical conducting material being of cylindrical shapewith a pair of notches on opposite sides of each core member definingspaced apart semi-cylindrical legs of the core member joined at one endby a base, one of said core members being rotatable relative to theother for mutual angular displacement around a common axis, and said tapchanging system comprising:

at least one field winding on each of the legs of the core membershaving a plurality of coil sections;

a tap connection at each end of each of said coil sections; and

switching means for selectively connecting each tap 11 connection to anadjacent tap connection of a coil section of said field windings on thesame core member whereby said coil sections are connected in series orparallel or a combination of both.

2. A tap changing system as claimed in claim 1, wherein said switchingmeans comprises:

a receptacle with a plurality of female terminals, each one of said tapconnections connected to a female terminals;

aplug adapted to be engaged in said receptacle;

a plurality of prongs on said plug, each prong adapted to be engaged inone of said female terminals; and

means for interconnecting said prongs in such a manner that said coilsections are connected in series or parallel or a combination of both.

3. A tap changing system as claimed in claim 1, including means forconnecting a source of alternating potential to said field windings onthe same core member; and

means for connecting a load to said field windings of the other coremember.

4. A tap changing system as claimed in claim 1, including means forgalvanically connecting said field windings in series.

5. A tap changing system as claimed in claim 1, wherein said fieldwindings are kidney-shaped in cross-section and dimensioned to snuglyfit on the legs of the core member.

6. A tap changing system as claimed in claim 1, wherein said fieldwindings on the legs of the rotatable core member are the secondarywindings of the transformer and said field windings on the legs of theother core member are the primary windings of the transformer and saidswitching means comprises:

a secondary receptacle with a plurality of female terminals, each one ofsaid tap connections of said coil sections of said secondary windingsbeing connected to a different female terminal;

a secondary plug adapted to be engaged in said secondary receptacle;

a plurality of prongs on said secondary plug, each prong adapted to beengaged in one of said female terminals and means for interconnectingsaid prongs on said secondary plug in such a manner that said coilsections of said secondary windings are connected in series or parallelor a combination of both;

a primary receptacle with a plurality of female terminals each one ofsaid tap connections of said coil sections of said primary windingsbeing connected to a diiferent female terminal;

a primary plug adapted to be engaged on said primary receptacle;

a plurality of prongs on said primary plug, each prong adapted to beengaged in one of said female terminals; and

means for interconnecting said prongs on said primary plug in such amanner that said coil sections of said primary windings are connected inseries or parallel or a combination of both.

References Cited UNITED STATES PATENTS 1,831,886 11/1931 Ross 3316-147X2,118,291 5/1938 Bollman 336147X 2,585,050 2/1952 Simon 336-X 2,609,4919/1952 Kirchner 336-X 2,609,531 9/1952 Kirchner 336-120X 3,016,4841/1962 Mulder et a1 336147X FOREIGN PATENTS 1,517,620 2/1968 France336-- 275,253 8/1951 Switzerland 336120 0 THOMAS J. KOZMA, PrimaryExaminer U.S. Cl. X.R.

